Physicochemical and microbial metabolic insights into o-xylene biotransformation mediated by catechol-type intermediate pathways in porous-packed biofilter.

In this study, gaseous o-xylene was removed using a laboratory-scale biotrickling filter packed with polyurethane foam cubes. The maximum elimination capacity of 35.36 g/(m3·h) can be achieved at an inlet concentration of 0.89 g/m3, a flow rate of 0.25 m3/h, and an empty bed residence time of 76 s. The adsorption of o-xylene by the packing medium followed the Freundlich isotherm model, and approximately 64% of the o-xylene carbon was mineralized to CO2 during steady-state operation, with the remainder utilized by microorganisms. Tax4Fun-based metabolic reconstruction revealed a 22.3% enrichment of xenobiotic biodegradation pathways in the biofilm community relative to the planktonic phase, with the xylene degradation pathway (ko00622) enriched 1.33-fold. The o-xylene catabolic pathway was reconstructed: upper-pathway methyl activation by toluene/o-xylene monooxygenase, nearly exclusive to the biofilm; ring cleavage through hierarchical dioxygenases spanning meta-, ortho-, and gentisate routes; and lower-pathway integration into the tricarboxylic Acid cycle (TCA). Pseudomonas, Mycobacterium, and Comamonas were identified as potential functional genera. The near-absence of anaerobic benzylsuccinate pathway enzymes exclusively aerobic degradation. Metabolism-related functions dominated the biofilm functional profile (75.02%). o-Xylene metabolism occurred predominantly on the packing-media biofilm rather than in the circulating solution, which indicated that enriching a metabolically specialized biofilm on high-surface-area porous packing is the key to efficient and stable performance. This study provides a scientific foundation for developing volatile organic compounds prevention and control strategies.